<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    .father {
        width: 400px;
        height: 400px;
        background-color: green;
        margin-top: 20px;
        border: 1px solid red;
    }

    .son {
        width: 200px;
        height: 200px;
        background-color: rgb(128, 62, 0);
        margin-top: 50px;
    }
</style>

<body>
    <div class="father">
        <div class="son"> </div>
    </div>
</body>

</html>